Creating buffers

If you've ever seen a map of an earthquake you might recall seeingrings around the quake's epicenter, showinghow far away the tremors were felt.Those rings were the result of a buffer analysis.Creating buffers around elements on your map is a very common geoprocessingtask that is useful for a wide variety of analysis and display purposes.Basically a buffer identifies regions that are within a certain distanceof any point, line, or polygon feature that's in your map.The buffer tool creates new polygonsthat surround the identified features, and thereare a couple of different tools in the arc toolbox, that'll help create them.

Now if you're toolbox isn't open.Go ahead and open up the Arc toolbox here.So we're going to use our map of dairy locations withinWashington state and precisely identify what areas are near the farms.I'm going to go into the analysis tools here,into proximity, and I'm going to choose this buffer tool.The buffer tool requires some input features.Those are going to be our dairy points, so drag, and drop them into input features.The output feature class is where we're going tosave this, so let's go ahead and press browse here.I'm going to come into my working folder here within the data files folder.

We'll create a new geo database, and I'm going to call this buffer.I'll double click to go inside of the buffergeo database, and here we're going to call this dairy rings.Go ahead and say Save, and now we can tell it how far out we want the rings to be.In this case I want to see all the areas that are within 20 miles of a farm.So I'm going to choose the linear unit of 20,and change this drop down list here, to miles.All of the other fields can be left theway they are so go ahead and just say okay.So when it gets done we can see all ofthe areas that are within 20 miles of a dairy farm.Maybe this area will help us identify sites where we need to focus soil orwater monitoring efforts to ensure that thedairy operations aren't adversely impacting the local environment.

The buffer technique can also help us locate the bestsites for a new farm supply store or feed silos.But buffers don't have to just be used for analysis work.They can also be used to achieve certain cartographic effects.One way that I've seen them used is to create what are calledwater vignettes that you might have seen on an old style nautical chart.For this we'll use a built-in script that will run the buffer tool multiple times.It's also found in the toolbox under proximity,and it's this one here this multiple ring buffer.The multiple ring buffer tool can be a bitprocessor intensive and it might take a while to run.

So lets just do a sample run on a few islands in San Juan county.I'm going to go ahead and turn off mydairy rings and also the dairy points here.I'm going to go to my bookmarks and choose San JuanCounty to zoom into the islands that we're interested in here.I'll start by using the polygon selection tool here,to select just a few islands in the county.Now it doesnt matter if you select exactly the same islands as I am.If you grab a few extra, or leave some out, that'll be just fine.The goal here is just to limit the features the tool'sabout to run on, so that it speeds up processing time.I've gone ahead and selected a few of the islands,and I actually selected one of the counties as well.

So I'm going to choose The featureselection tool, back to the rectangle and I'mgoing to shift click to deselect the countyboundary here and also over here as well.Now that I have some islands selected I'll right click on the Washingtonshape layer going down to selectionand choose create layer from selected features.That'll add just those islands to the map by themselves.And I can go ahead and turn off the rest of Washington here.So now I have just a few islands to run the multiple ring buffer tool against.I'll double click on multiple ring buffer to start the tool.And I'm going to go ahead and take this Washington selection,those are just the islands and drag those into the input features.

The output feature class, I'll click on thebrowse button, in my buffer geodatabase that I created.I'm going to call this water vignette.Go ahead and say Save and now we're going tospecify how far out we want the rings to occur.I'm going to put in the first one at 500 feet andpress the plus button and that'll add it to a list here.The next one is going to be 500 feet further out so it'll be at 1,000 feet.Go ahead and say plus, the next one will be 1,000feet out from that so that'll put it at 2,000 feet.I'll press plus.The next one is 1500 feet further.So it'll be at 3500 feet.

I'll press plus.And then finally, we'll have one 2000 feet furtherout from that, which will put us at 5500 feet.Go ahead, press plus again.I'm going to scroll down the list a little bit.And make sure that the buffer either says default, or changeit to feet, which is the default units for this particular map.We'll go ahead and say okay to run the tool.The multiple ring buffer tool will take just a moment to run.When it finishes, we'll get the symbology ofall these different polygons that are around our islands.Let's go ahead and drag this selection on top of the water vignette layer.And now we'll go ahead and symbolize the water vignettes.

I'll double click on it to open the Property sheet.And in Symbology, I'm going to click onthis header here and choose Properties for All Symbols.Here I can choose this hollow property to make them with no fill.And I'll change the outline color to a bright blue color, here.Let's go ahead and say okay.Apply.And I'll say okay again.And so now you can see we have multiple ringbuffers around our islands, which highlight this kind of water effect.So that's how the buffer tool works.The buffer geoprocessing tools offer another easyway to create additional geometries in yourmaps that can aid further analysis effortsor just create that finishing cartographic touch.

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3/11/2014

Get up and running with ArcGIS, a true geographic information system (GIS) that allows you to dig into highly accurate geospatial data in a way other mapping applications can't compete with. It's great creating maps, analyzing data for land use studies and other reports, and preparing data for use in an application or database. Let Adam Wilbert show you how to display, analyze, and illustrate geospatial data with ArcGIS. He explores how to import data from multiple sources, manage it with the ArcGIS catalog, and then start making maps. Learn how to lay out your data in the ArcMap component; add symbols, scale bars, and legends; and get your maps out of ArcGIS and into the real world, whether it's for printing or export to another application.